Bituminous binder compositions are used in road construction in order to provide bonding between the aggregates or between the substrate and the aggregates. Various methods are employed for road construction using bituminous binder compositions and aggregates as is disclosed in for example U.S. Pat. No. 6,156,113, incorporated by reference herein.
Bituminous binder compositions may comprise bitumen, elastomers and/or solvents. The bitumen may either be straight run products or processed products (cf. Kirk-Othmer, Encyclopedia of Chemical Technology, 4th Ed., Vol. 3, pages 689-724).
Elastomers are usually added to the bituminous binder composition to improve properties, e.g. rutting resistance, of the bitumen. Reference is for example made to U.S. Pat. No. 4,242,246, incorporated by reference herein. Also cohesion of porous asphalt layers is improved thus reducing the degradation thereof by ravelling, i.e. separation of the aggregates from the asphalt surface. Finally, elastomers are necessary to obtain a strong, yet flexible and sufficiently plastic binding material. Although elastomers are sufficiently compatible with bitumen, they are detrimental to processability in that they cause a too high viscosity. In some cases this requires the addition of solvents and/or fluxing oils to lower the viscosity and to improve solubility of the elastomers in the bitumen and the processing and application of the bituminous binder composition.
In surface dressing applications first bituminous binder compositions are sprayed on the road surface followed by adding aggregates. Obviously, the viscosity of the bituminous binder composition must be sufficiently low to ensure proper processability and the formation of a uniform layer of the composition on the road surface. However, under these conditions solvents and/or fluxing oils that are necessary to control the viscosity lead to health, environmental and safety problems due to their high volatility and flammability. Vapours may for example be inhaled by operators. Also, vapours contribute to environmental pollution by photochemical oxidation (smog formation) and the greenhouse effect. Likewise, transport of such highly volatile and flammable solvents containing bituminous binder compositions becomes more and more restricted.
It is proposed in the art to replace highly volatile and flammable solvents by less volatile and flammable liquid products, e.g. vegetable oils. For Example, EP A 568.757, incorporated by reference herein, discloses the replacement of solvents with an animal and/or vegetable fat or oil and/or with a mixture of such substances. A binder prepared in this way is said to have the advantage over known binders that it does not contribute to atmospheric pollution. However, the use of such less volatile and flammable liquid products often leads to a too low softening point of the asphalt during its service life leading to “blackening up” of the asphalt layer.
“Blackening up” can be described as follows. When chippings in a chip seal layer are able to move and roll they will get covered by a binder layer. As a result, the road surface will acquire a relatively uniform surface of chippings and binding layer, said surface having a black appearance. The rolling of chippings may be caused by too low visco-elasticity of the binder as a result of either high road surface temperatures or poor thermal material properties. To prevent “blackening up”, a binder must have a sufficiently high softening point in combination with the appropriate visco-elastic properties at the higher service temperatures, i.e. temperatures prevailing during hot summers.
Another feature related to “blackening up” is that rolling can occur when a too high amount of binder is used in comparison to the average size distribution of the chippings. Under high traffic loads or high environmental temperatures chippings penetrate the binder layer more and more and eventually are absorbed by the binder.
The disadvantage of “blackening up” can for example be avoided by including a cross-linkable polymer or curable solvent in the bituminous binder composition, said cross-linkable polymer or curable solvent being hardened under the influence of oxygen, UV radiation and transition metal catalysts. For example, U.S. Pat. No. 6,156,113 discloses a bituminous binder composition comprising bitumen, a fatty acid monoester and a catalyst, wherein the catalyst is a transition metal salt such as cobalt octoate, cobalt naphtenate and zirconium octoate. Such catalysts are also known in the art as siccatives. However, these transition metal salts have an adverse effect on the environment and are therefore less desirable. In many countries the use of such catalysts in construction materials is severely restricted by law or even prohibited by law because of their long term negative environmental impact. In addition, bituminous binder compositions have a low permeability for oxygen so that the cross-linking reaction proceeds relatively slowly. U.S. Pat. No. 6,156,113 discloses that a significant increase of the initial ring-and-ball softening point of the bituminous binder composition is only achieved after about 30 days (cf. in particular the Figure). Obviously, such bituminous binder compositions need a considerable period of time to attain the required strength and other required properties.
Another option for solving the problems associated with “blackening up” is to increase the temperature dependence of the properties of the bituminous binder composition. As will be clear to the person skilled in the art, a low viscosity is desired at high temperatures so that the bituminous binder composition can easily be applied during road construction whereas at low temperature, e.g. during service, a high viscosity is desired to ensure sufficient strength and adhesion.
WO 00/73378, incorporated by reference herein, discloses a storage stable bitumen binder composition comprising 75-99.95 wt. % of bitumen, 0 to 15 wt. % of an elastomer and 0.05-10 wt. % of an amide additive, preferably 85-99.4 wt. % of bitumen, 0.5-12 wt. % of the elastomer and 0.1-3 wt. % of the amide additive.
WO 030/062315, incorporated by reference herein, discloses a binder composition that can be used in asphalts wherein the binder composition comprises 1-70 wt. % of a resin, 20-97 wt. % of a lubricating oil or a lubricating oil extract and 0.1-3 wt. % of an amide additive. The resin is preferably an elastomer such as styrene-butadiene-styrene. The lubricating oil or lubricating oil extract may be selected from a wide range of products including those obtained from refinery processes and vegetable oils. However, it is preferred that the lubricating oil or lubricating oil extract is obtained by solvent extraction of a deasphalted oil, in particular a bright-stock furfural extract. Table 1 of WO 030/062315 discloses that the addition of 1.0 wt. % of the amide additive ethylene bisstearamide (EBS) results in an increase of the ring-and-ball softening point of 4° C.
However, the bituminous binder compositions according to the prior art are still deficient in terms of the temperature dependence of the viscosity.